Alkalis & Bases

Definition  

- Bases → substances that neutralise acids.  

- Alkalis → a special group of bases that are soluble in water and are salts of alkali metals or alkaline earth metals.  

- Alkali compounds release hydroxyl ions (OH⁻) when dissolved in water.  

Common Alkalis & Uses  

- Magnesium hydroxide (Mg(OH)₂) → Milk of Magnesia (antacid).  

- Sodium hydroxide (NaOH) → used in soap making.  

- Ammonium hydroxide (NH₄OH) → window cleaning solution.  

- Potassium hydroxide (KOH) → also used in soap production.  

- Calcium hydroxide (Ca(OH)₂) → lime water.  

Strength of Bases  

- Strong Bases → completely ionise in water.  

  - Sodium hydroxide (NaOH).  

  - Potassium hydroxide (KOH).  

  - Calcium hydroxide (Ca(OH)₂).  

- Weak Bases → partially ionise in water.  

  - Ammonium hydroxide (NH₄OH).  

  - Ammonia (NH₃).  

  - Zinc hydroxide (Zn(OH)₂).  

General Reaction  

Soluble base + salt → insoluble base + salt  

Key Takeaway:  

All alkalis are bases, but not all bases are alkalis. Strong bases fully dissociate, while weak bases only partially do so. Alkalis are widely used in everyday products like soaps, cleaning agents, and medicines.